Have you tried a different HDMI cable just in case that's faulty?
If that doesn't work then it seems you have the green screen of death and will need a box replacement.
It's not the words you want to hear, but the quickest method is using the phone unfortunately.
That's 150 from a Virgin landline, or 0345 454 1111, options 1,1 and 2 (Faults) butbest to call at 8am to avoid call queues or around tea time.
When calling Faults you will get the automated response asking you to press 1 for the link to online support, ignore the options and don't press any buttons then you should be placed into a queue and an agent should pick up the phone and resolve the problem.
You could also try the text messaging service. Just send a text with a description of TV Faults to 07533 051809. Your message will go into a queue and a representative will respond to you as soon as possible.It may take a few days.
Forum Staff can take between a few days to a week to pick up your issue here.
The Service you do for others is the rent you pay for your room here on Earth - Muhammad Ali